1. Field of the Invention
This invention relates generally to superabrasive cutting elements, inserts, or compacts, for abrasive cutting of rock and other hard materials. More particularly, the invention pertains to improved interfacial geometries for polycrystalline diamond compacts (PDCs) used in drill bits, reamers, and other downhole tools used to form a borehole in a subterranean formation.
2. Background of Related Art
Drill bits for oil field drilling, mining and other uses typically comprise a metal body into which cutting elements are incorporated. Such cutting elements, also known in the art as inserts, compacts, buttons, and machining tools, are typically manufactured by forming a superabrasive layer on the end of a sintered or cemented tungsten carbide substrate. As an example, polycrystalline diamond, or other suitable superabrasive material, such as cubic boron nitride, may be sintered onto the surface of a cemented carbide substrate under ultra-high pressure and ultra-high temperature to form a PDC, or other polycrystalline compact. During this process, a sintering aid such as cobalt may be premixed with the powdered diamond or swept from the substrate into the diamond table. The sintering aid also acts as a continuous bonding phase between the diamond table and substrate.
Because of different coefficients of thermal expansion and bulk modulus, large residual stresses of varying magnitudes, at different locations, may remain in the cutting element following cooling and release of pressure. These complex stresses are concentrated near the superabrasive table/substrate interface. Depending upon the cutting element construction, the direction of any applied forces, and the particular location within the cutting element under scrutiny, the stresses may be either compressive, tensile, shear, or mixtures thereof. In the superabrasive table/substrate interface configuration, any nonhydrostatic compressive or tensile load exerted on the cutting element produces shear stresses. Residual stresses at the interface between the superabrasive table and substrate may result in failure of the cutting element upon cooling or in subsequent use under thermal stress and applied forces, especially with respect to large-diameter cutting elements. These manufacturing-induced stresses are complex and are of a nonuniform nature and thus often undesirably place the superabrasive table of the cutting element into tension at locations along the superabrasive table/substrate interface.
During drilling operations, cutting elements may be subjected to very high forces in various directions, and the superabrasive layer may fracture, delaminate, spall, or fail due to the combination of drilling-induced stresses as well as residual stresses much sooner than would be initiated by normal abrasive wear of the superabrasive layer. Because a tendency toward premature failure of the superabrasive layer and failure at the superabrasive table/substrate interface may be augmented by the presence of high residual stresses in the cutting element, many attempts have been made to provide PDC cutting elements which are resistant to premature failure. For instance, the use of an interfacial transition layer with material properties intermediate of those of the superabrasive table and substrate is known within the art. Also, the formation of cutting elements with noncontinuous grooves or recesses in the substrate filled with superabrasive material is also practiced, as are cutting element structures having interfacial concentric circular grooves or a spiral groove.
The patent literature reveals a variety of cutting element designs in which the superabrasive table/substrate interface is three dimensional, i.e., the superabrasive layer and/or substrate have portions which protrude into the other member.
U.S. Pat. No. 5,351,772 of Smith shows various patterns of radially directed interfacial structures on the substrate surface; the formations project into the superabrasive surface. More particularly, a cutting element interface having inner spokes that radially extend circumferentially between outer spokes is shown in FIG. 6A thereof.
As shown in U.S. Pat. No. 5,486,137 of Flood et al., the interfacial superabrasive surface has a pattern of unconnected radial members which project into the substrate; the thickness of the superabrasive layer decreases toward the central axis of the cutting element.
U.S. Pat. No. 5,590,728 of Matthias et al. describes a variety of interface patterns in which a plurality of unconnected straight and arcuate ribs or small circular areas characterizes the superabrasive table/substrate interface.
U.S. Pat. No. 5,605,199 of Newton teaches the use of ridges at the interface which are parallel or radial, and includes a ring of greater thickness than the remaining superabrasive table proximate the radial periphery thereof.
In U.S. Pat. No. 5,709,279 of Dennis, the superabrasive table/substrate interface is shown to be a repeating sinusoidal surface about the axial center of the cutting element.
U.S. Pat. No. 5,871,060 of Jensen et al., assigned to the assignee hereof, shows cutting element interfaces having various ovaloid or round projections. The interface surface is indicated to be regular or irregular and may include surface grooves formed during or following sintering. A cutting element substrate is depicted having a rounded interface surface with a combination of radial and concentric circular grooves formed in the interface surface of the substrate.
U.S. Pat. No. 6,026,919 of Thigpen et al. discloses, in FIG. 10 thereof a cutting element comprising concentric ring structures formed in the substrate thereof, wherein radial grooves extend from the center of the cutting element to the radial edge thereof, through each ring structure.
U.S. Pat. No. 6,315,067 of Fielder discloses, in FIG. 4 thereof, concentric ring structures formed in a substrate of a cutting element, wherein the members comprising the ring structures are substantially circumferentially aligned.
U.S. Pat. No. 6,571,891 to Smith et al., assigned to the assignee of the present invention and the disclosure of which is incorporated herein in its entirety, discloses concentric ring structures formed in a substrate of a cutting element, wherein the members comprising the ring structures are substantially circumferentially aligned. Similarly, U.S. Pat. No. 6,739,417 to Smith et al., assigned to the assignee of the present invention and the disclosure of which is incorporated herein in its entirety, discloses concentric ring structures formed in a substrate, including a substantially cylindrical PDC-type substrate having a substantially planar surface and a stud-type substrate having a generally domed surface, of a cutting element, wherein the members comprising the ring structures are substantially circumferentially aligned.
Drilling operations subject the cutting elements on a drill bit to extremely high stresses, often causing crack initiation and subsequent failure of the superabrasive table. Much effort has been devoted by the industry to making cutting elements resistant to rapid deterioration and failure.
Each of the above-indicated references, the disclosures of each of which are hereby incorporated herein, describes three-dimensional superabrasive table/substrate interfacial patterns which may ameliorate certain residual stresses in a cutting element. Nevertheless, the tendencies of the superabrasive table to fracture, defoliate, and delaminate remain. Accordingly, an improved cutting element having enhanced resistance to such stress-induced degradation is needed in the industry.